The invention is directed to an improved and apparatus for enhancing vehicle traction and skid resistance.
By means of the known possibility of combining an anti-skid system (ABS) with traction control (ASR), it is possible for existing components such as wheel sensors, control elements and the like, provided for ABS operation, to be used for traction control as well, thus expanding the possibilities of the ABS system. See, for example, the article entitled "Systeme antiblocage avec fonctions elargies"[Anti-skid system with expanded functions] by Erich Reinecke, published in the journal "Ingenieurs de l'Automobile"[Automotive Engineers], pages 110-116. The basic functions of an ABS system expanded to include traction control is then that even during startup, a control of the wheel movements is effected, although in more or less the reverse direction from what is done in the ABS system, in that the sensors provided for the ABS system detect any spinning of (driven) wheels and by triggering suitable control elements assure that the brake pressure for the spinning wheel is increased, so that this wheel is braked until normal grip of the wheel on whatever road surface is present is re-established. Traction control of this kind is not only advantageous for preventing high-powered passenger cars from spinning their wheels on starting up, but is also preferentially used for increasing traction and improving roadability especially in winter driving conditions, so that even on icy or snowy slopes starting up is still possible, and spinning of one of the driven wheels can be avoided, should that wheel happen to be on a surface having a low coefficient of friction. This traction controller, known generally as anti-skid reduction (or ASR) accordingly works somewhat like a locking differential, but avoids the disadvantages of that device, and as a way to increase traction and roadability of motor vehicles it is also favorable from the cost standpoint because it makes further use of components already present for ABS systems.
To increase the coefficient of friction, especially under winter driving conditions, it is also known (see publication VDT-UBB 160 (10.56), "Bosch-Splittstreuer" [Bosch Gravel Spreader], Robert Bosch GmbH, Stuttgart, Federal Republic of Germany), to dispose gravel bins ahead of at least the driven wheels of motor vehicles, especially trucks or buses, so that upon separate manual actuation of a pushbutton or switch by the driver, and therefore dependent upon his decision, gravel can be spread ahead of driven wheels as needed, over relatively short or not so short distances. To this end, a rotary slide actuated by compressed air via an electromagnetic control valve is associated with each gravel spreader container and also actuates a shaft for breaking apart clumped-together gravel.
A similar effect can be achieved by using centrifugal chains (see the journal, Nutzfahrzeug [Utility Vehicle], Nov. 1986, pages 52-54), which can be disposed in various ways in the region of the driven wheels of motor vehicles, primarily buses or trucks, in such a way that on the one hand the driver is spared the tedious work of putting on the chains on hills and the like, yet by arbitrary switch actuation the chains can be deployed ahead of the wheels to increase the traction. Such systems may have a pneumatic swivel mechanism for the chains. Electromechanical systems with so-called Rotogrip chain mats are also known, however. Gravel spreaders and chains improve braking under winter conditions, especially on icy hills and the like, and can also be used together with antiskid systems, as disclosed in published European Patent Application 0078392. In a road vehicle equipped with an anti-skid system, a gravel spreader is switched on automatically whenever the ABS system responds, although to save gravel the actuation does not occur until the pressure difference upstream and downstream of the regulating valves exceeds a certain magnitude and the coefficient of friction is also correspondingly low. To detect the pressure difference, a differential pressure converter is provided, followed on the output side by an evaluation circuit.
Other systems comparable to the gravel spreader are known as sand spreaders (British Patent 2,040,838 and U.S. Pat. No. 3,797,867), where by actuation of a foot or manual switch from the driver's compartment, either sand from a central storage bin can be spread ahead of the driven wheels by gravity (British Patent 2,040,838), or the friction-promoting agent is sprayed ahead of the driven wheels from the sand bin pneumatically by the generation of an air flow.